This invention relates to a vibration relief apparatus and a magnetic damper mechanism therefor, and more particularly to a vibration relief apparatus suitable for use as a suspension unit for a seat for a conveyance such as an automobile, an electric railcar, a ship or the like and a magnetic damper mechanism suitable for use for such a vibration relief apparatus.
A variety of damping materials, dampers and damping techniques have been conventionally proposed as a measure to counter vibration and noise of a machine or a structure which is typically constructed of a material reduced in internal damping in order to ensure rigidity thereof.
In particular, remarkable development of a conveyance at a high velocity or speed which has been recently made causes damage to the human body and nerve due to exposure of the body to vibration of the conveyance. Such damage is generally expressed in the form of a symptom such as fatigue, headache, shoulder stiffness, lumbago, amblyopia or the like. In general, isolation of vibration is carried out by means of a suitable combination between a spring such as a metal spring, an air spring, a rubber material or the like and a damping material such as a viscoelastic material, a damper or the like. However, such a combination generally leads to such antinomic relationship as seen between, for example, a kinematic magnification and a loss factor. More specifically, a reduction in kinematic magnification for the purpose of improving low-frequency characteristics causes a spring to be decreased in loss factor, to thereby be hard, leading to a deterioration in high-frequency characteristics. Whereas, an increase in loss factor in order to improve high-frequency characteristics causes the spring to be increased in kinematic magnification, to thereby be soft, leading to a deterioration in low-frequency characteristics as in a damping material. Thus, many attempts were made to restrain vibration using a passive damping device or by quasi-active controlling or active controlling.
Under such circumstances, a suspension unit constructed as shown in FIGS. 18 and 19 was proposed as a seat for reducing vibrational energy of a conveyance. More specifically, the suspension unit generally designated at reference numeral 100 in FIGS. 18 and 19 includes a compressed coil spring 104 arranged between a lower frame 102 and an upper frame 103 coupled to each other through a linkage 101. Also, it includes a shock absorber 105 arranged therebetween so as to act as a viscous damping mechanism.
In the conventional suspension unit 100 thus constructed, the compressed coil spring 104 is configured so as to exhibit a relatively large spring constant around or about an equilibrium point in order to permit support load at a required level to be provided at a position of the equilibrium point. Also, the suspension unit 100 includes a spring 106 such as a torsion bar or the like arranged for adjusting a difference in load mass or body weight to render the position of the equilibrium point constant. Such arrangement of the spring 106 causes a spring constant of the spring 106 to be added to that of the compressed coil spring 104, resulting in a spring constant of a spring system about the equilibrium point to be increased to a level as high as, for example, k=20 N/mm. This leads to an increase in frequency band at a resonance point, to thereby cause an increase in transmissibility of vibration, resulting in load applied to the human body due to vibration during traveling of a conveyance or vehicle being enhanced, so that a symptom such as fatigue, car sickness or the like may be readily caused.
Recently, a magnetic damper has been frequently incorporated as a damping unit in a suspension unit, an engine mount or the like. The magnetic damper effectively acts as a damping force element. However, the conventional magnetic damper is highly reduced in magnetic flux density to a level substantially below 1T, resulting in being increased in velocity or speed dependency thereof, leading to a failure to produce enhanced damping force in a low velocity region.
The present invention has been made in view of the foregoing disadvantage of the prior art.
As a result of a careful study by the inventors, it was found that horizontal holding of a metal spring on a linkage for connecting one of a pair of frames or a lower frame and the other frame or an upper frame to each other permits a spring constant of a spring about an equilibrium point to be provisionally or falsely set at a value near zero (0) while employing a metal spring as the spring.
Accordingly, it is an object of the present invention to provide a vibration relief apparatus which is capable of reducing a frequency at a resonance point, to thereby decrease vibration transmissibility thereof in a high frequency region, resulting in improving a feeling in riding.
It is another object of the present invention to provide a vibration relief apparatus which is capable of being suitable for use for a suspension unit for a conveyance.
It is a further object of the present invention to provide a magnetic damper which is capable of producing damping force at an increased magnitude even at a low speed of a conveyance, to thereby be suitable for use for the above-described vibration relief apparatus.
In accordance with one aspect of the present invention, a vibration relief apparatus is provided. The vibration relief apparatus includes a linkage including a pair of frames. The other of both frames is arranged so as to be vertically movable with respect to one of the frames. The vibration relief apparatus also includes a first spring mechanism constituted of a plurality of metal springs substantially horizontally held on the linkage, holding a position of an equilibrium point and exhibiting negative spring characteristics below the equilibrium point, and a second spring mechanism for generating lifting force for adjusting a load mass difference with respect to the other frame. The first spring mechanism and second spring mechanism cooperate with each other to provide a spring system. The spring system has a superposed spring constant falsely set to be near zero about the equilibrium point.
In a preferred embodiment of the present invention, the linkage includes link members, wherein the metal springs constituting the first spring mechanism each are a tension coil spring for forcing the link members of the linkage in a direction in which the link members are closed.
In a preferred embodiment of the present invention, the metal springs each are formed by connecting a plurality of coil springs to each other in series.
In a preferred embodiment of the present invention, the second spring mechanism is constituted of a torsion bar.
In a preferred embodiment of the present invention, the vibration relief apparatus further includes a shock absorber including a piston rod and a cylinder, wherein one of the piston rod and cylinder is connected to the one frame and the other thereof is connected to the other frame.
In a preferred embodiment of the present invention, the vibration relief apparatus further includes a magnetic damper mechanism.
In a preferred embodiment of the present invention, the magnetic damper mechanism includes a pair of permanent magnets and an operation member. The permanent magnets each are constituted by a multipole magnet. The operation member is arranged so as to cross a leakage magnetic field formed at a boundary between N poles of the permanent magnets and S poles thereof when it relatively moves in a gap formed between the permanent magnets depending on vibration.
In a preferred embodiment of the present invention, the vibration relief apparatus further includes a shock absorber including a piston rod and a cylinder, wherein one of the piston rod and cylinder is connected to the one frame and the other thereof is connected to the other frame.
In accordance with another aspect of the present invention, magnetic damper mechanism which is adapted to exhibit damping performance by electromagnetic induction is provided. The magnetic damper,mechanism includes a pair of frames arranged opposite to each other, a pair of permanent magnets fixed on one of the frames and spaced from each other so as to be opposite to each other in an attracting direction, and an operation member made of a material reduced in electrical resistivity and fixedly arranged on the other of the frames so as to relatively move in a gap between the permanent magnets depending on vibration. The operation member is arranged so as to cross a leakage magnetic field formed at a boundary between N poles of the permanent magnets and S poles thereof when it relatively moves in a gap formed between the permanent magnets depending on vibration.